1. Field of the Invention
The present invention relates to a tilt sensor (tiltmeter) provided with a sealed container which is comprised of a container body and a top cover plate (upper end plate) which closes the container body and is provided with a recess whose depth gradually increases from the peripheral portion thereof toward the center portion, and a liquid enclosure containing therein an air bubble, which is enclosed in the container body.
2. Description of the Related Art
In general, a tilt sensor is provided in survey instruments, aircraft, or automobiles, etc., to measure the tilt angle thereof. The tilt sensor includes a sealed container which is comprised of, for example, a top cover plate in the form of a circular disc which is provided with a recessed surface, a circular bottom plate, and a cylindrical body. The cylindrical body is closed at the upper and lower open ends thereof by the top cover plate and the bottom plate, respectively. The position of an air bubble contained in a liquid enclosed in the sealed container is electrically detected.
To facilitate the mounting operation of the top cover plate and the bottom plate to the cylindrical body, the top cover plate, the bottom plate, and the cylindrical body are circular in a plan view, so that, upon the mounting operation, the axis of the top cover plate and the bottom plate can be easily aligned with the axis of the cylindrical body with reference to the configuration (outer shape) of the three elements.
The top cover plate is provided on one surface thereof with a recess formed, for example, by a part of a spherical surface. The recess permits an air bubble contained in a liquid enclosed in the sealed container to move in accordance with the inclination of the container body. The recess is constructed so that when the top cover plate is coaxially connected to the cylindrical body, the line normal to the recess at the deepest portion thereof is identical to the center of the configuration of the top cover plate, that is, the outer peripheral edge of the recess concurs with the inner peripheral edge of the cylindrical body.
The top cover plate can be made of a glass mold. In case of a top cover plate of a glass mold, the center of the configuration of the top cover plate may deviate from the normal line (axis) at the deepest portion of the recess, depending on the precision of the molding dies. In this connection, if the top cover plate whose center of configuration is not located at the deepest point of the recess is mounted to the cylindrical body with reference to the configuration of the top cover plate and the cylindrical body, a slight gap or clearance may be produced between the top cover plate and the cylindrical body. Consequently, the outer periphery of the top cover plate must be ground to make the center of the configuration of the top cover plate coincident with the normal line at the deepest point of the recess. This operation will be referred to hereinafter as a centering operation (grinding operation). The centering operation is carried out by grinding the outer peripheral edge of the top cover plate while rotating the top cover plate about the normal line at the deepest point of the recess, as in the grinding operation of an optical lens. To this end, it is necessary to align the center (axis) of rotation of the top cover plate with the normal line at the deepest point of the recess thereof (referred to as an aligning operation), prior to the centering operation, as in the case of an optical lens.
In the machining of an optical lens, the aligning operation is carried out by a bell chuck (bell clamp) system or a center detection method using a laser beam. The bell chuck system refers to a clamping system of a lens using cylindrical bell chucks which movably hold opposite surfaces of the lens, wherein the relative sliding movement between the lens and the bell chuck along a spherical surface of the lens takes place, so that the lens can be firmly held in a stable position in which the entire periphery of each end edge of the bell chuck comes into contact with the corresponding surfaces of the lens. The center detection method using a laser beam refers to a detection method in which the lens held by, for example, the bell chuck system is illuminated with the laser beam, so that the center of the lens can de detected in accordance with the light transmitted through or reflected by the lens.
However, the bell chuck system or the center detection method using the laser beam, as mentioned above cannot be properly used for the aligning operation of the top cover plate. Namely, in the aligning operation by the bell chuck system, it is necessary to slide the top cover plate relative to the bell chuck while bringing one front end edge of the bell chuck into contact with the recess of the top cover plate. However, since the recess of the top cover plate is usually defined by an optically rough surface, no smooth sliding movement of the top cover plate occurs. Moreover, if the recess of the top cover plate is defined by a toroidal surface, an end edge of the bell chuck is always in partial contact with the recess of the top cover plate, and hence no smooth movement (sliding movement) of the top cover plate takes place whatever the curvature of the recess is.
Furthermore, center detection methods can not be used for the aligning operation of the top cover plate, since the laser beam cannot be transmitted through the recess of the top cover plate made of a rough surface.
Under these circumstances, in the prior art, the aligning operation of the top cover plate must rely upon the measurement with the operator's eyes, which is time consuming and troublesome.